Articles that have release characteristics are used in a variety of applications. Adhesive-coated articles (e.g., with a pressure-sensitive-adhesive), such as tapes, die-cuts, labels, and the like, often employ a release coating as a part of their structure. The purpose of the release coating is to provide a surface to which the adhesive coating does not permanently adhere. For tapes in roll form, the coating is oftentimes referred to as a low-adhesion backsize (LAB). In this form, the adhesive surface contacts the back surface of the article. The LAB prevents the adhesive from permanently adhering to the back surface of the article and allows that article to be unwound.
In the past, release coatings have been applied to surfaces by preparing the release components in solvent, coating the solution onto a desired surface, and drying to evaporate the solvent. One example of a release coating formed using a conventional solvent-based process is found in U.S. Pat. No. 2,532,011 (Dahlquist et al.). Dahlquist et al. teach low-adhesion coatings of polyvinyl carbamate polymers, wherein the side chains terminate with a long chain alkyl group (i.e., an alkyl group more than five carbon atoms in length). An example is polyvinyl N-octadecyl carbamate, made by reacting together polyvinyl alcohol and octadecyl isocyanate. Dahlquist et al. teach that the polyvinyl carbamates therein are soluble in volatile aromatic solvents and may readily be applied in solution form by simple coating procedures followed by drying to form solvent-free, continuous films.
Solvent-based processes, however, have become increasingly less desirable due to special handling concerns associated therewith. This has led to accelerated interest in the use of hot-melt extrusion coating of release materials, backings, adhesives and the like. For example, U.S. Pat. No. 4,379,806 (Korpman) discloses preparation of pressure-sensitive-adhesive tapes by a single-step process of co-extruding a backing film-forming composition and an adhesive composition. A solventless release agent may be incorporated into either the adhesive or backing, rendering unnecessary the coating of the backside of the tape with a release agent. Korpman states that suitable release agents for incorporation into backing films include synthetic and natural waxes and copolymers of stearyl methacrylate and acrylonitrile.
U.S. Pat. No. 4,626,460 (Duncan) describes a biaxially oriented label stock product having a facing layer and a release layer. The facing layer is co-extruded with the release layer. The facing layer has a pressure-sensitive-adhesive material incorporated therein. The release layer is a polyolefin film having a release agent component. Suitable release agents described therein are silicones, modified silicones, polyethylene, fluorocarbon, Werner-type chromium complexes and polyvinyl octadecyl carbamate.
U.S. Pat. No. 5,700,571 (Logue et al.) describes a release liner consisting of a first olefin polymer film formed having dispersed therein by high shear mixing a release substance (polyethyleneimine octadecyl carbamide, polyvinyl octadecyl carbamate, or a mixture thereof) that is co-extruded or co-cast onto a film formed from a second olefin polymer (i.e., polypropylene-based). The release additive material is dry blended into the first olefin polymer film by melt blending using a SIGMA blade, BANBURY mixer or the like. It is stated that good blending cannot be achieved in a single-screw extruder with any expectation of forming a coherent film due to the tendency of the release additive to remain as a discrete particulate solid. In other words, the required conditions of high shear cannot be achieved in a single-screw extruder. Thus, after dry blending, the product is transferred to a single-screw extruder, where it can then be co-extruded with a polypropylene polymer film or recovered as pellets and subsequently added to an extruder.
European Pate Application No. 0-484-093-A2 (Neste Oy) discloses a polymer composition for forming release films. The film is formed of a reactive polyolefin that contains functional groups and a reactive silicone or other reactive release substance. The ingredients are caused to react by compounding them together in a molten state. The reactive compounding can be performed in connection with the film preparation to form a release film. The film can be prepared by means of a blown-film, cast-film, or extrusion coating technique. A reactive polyolefin mentioned therein is an ethylene/hydroxyethyl methacrylate copolymer having 8 mole % hydroxyethyl methacrylate, commercially available from Neste Oy under the tradename NCPE0465.Release substances exemplified therein are silicone-containing substances, an epoxidized soybean oil, and an alkyl cetene dimer. It is stated that the quantity of the reactive release substance can vary within the range of 0.1-20% by weight, although a suitable quantity is purportedly selected within the range of 1-10% by weight. It is cautioned that when higher contents of the release substance are used, the reaction compound can become too cross-linked.
Conventional release materials, release-coated films and articles have not proven to be entirely satisfactory for certain applications. Obtaining an optimum balance between release performance, cost-effectiveness, solvent-reduction, and processing efficiency is desired.